The present invention relates generally to anti-racking means for the doors of large cargo containers and the like.
Large cargo containers and the like having enclosed bodies are conventionally provided with a rectangular door frame, a pair of doors which are adapted to be swung within the plane of the door frame for closing the latter, and rotary bar locking mechanism for selectively retaining the doors within the door frame. The door frame comprises horizontal top and bottom frame members and vertical side frame members suitably welded at their adjacent corner ends. For purposes of economy, the container (including the door frame) is usually fabricated of structural members having the least strength practical, and the doors are normally fabricated of plywood faced with an inner and an outer aluminum skin.
Because of the weakness of the structural members, the door frame is subject to considerable distortion when racking forces are applied to the container. The door frame is partially reinforced by the doors, and the frame and doors may be further reinforced by the rotary bar locking mechanism. However, such reinforcement has not been sufficient to withstand severe racking forces. For example, it has been observed that racking forces applied to the container diagonally at one corner of the door frame end tend to cause the top door frame member to assume a shallow sidewise S-curve with the maximum deflection occurring generally at the midpoint of the top frame member adjacent the gap of the doors. It has also been observed that such racking forces tend to cause an outward bowing of the vertical side frame members generally between the hinges.